My Dear Boys: This book is a complete story in itself, but forms the sixth volume in a line issued under the general title, "The Second Rover Boys Series for Young Americans." As noted in some volumes of the first series, this line was started years ago with the publication of "The Rover Boys at School," "On the Ocean," and "In the Jungle," in which I introduced my readers to Dick, Tom and Sam Rover and their relatives and friends. The twenty volumes of the First Series related the doings of these three Rover boys while attending Putnam Hall Military Academy, Brill College, and while on numerous outings. Having finished their education, the three young men established themselves in business and became married. Dick Rover was blessed with a son and a daughter, as was also his brother Sam, while Tom became the proud father of a pair of the liveliest kind of twin boys. From their home in New York City the young Rovers were sent to a boarding school, as related in the first volume of the Second Series, entitled "The Rover Boys at Colby Hall." From that institution of learning the scene was shifted to "Snowshoe Island," where the lads spent a mid-winter outing. Then they rejoined their fellow-cadets and had some strenuous doings while "Under Canvas." After that, in a volume entitled "The Rover Boys on a Hunt," I related how they uncovered the mystery surrounding a strange house in the woods. And following this came a trip to Texas and Oklahoma, where, "In the Land of Luck," the boys aided Dick Rover in his efforts to locate some valuable oil wells. In the present volume the scene is shifted back to Colby Hall and then to a ranch in the West where some remarkable happenings await our young heroes. From reports received I am assured that the sale of this line of books has now passed the _three million_ mark! This is as astonishing as it is gratifying. I sincerely trust that the reading of the volumes will do all of the boys and girls good.